create_session_cgroup() used to be called from run_bwrap()'s on_start
callback, in the parent, concurrently with the just-forked child execing
into bwrap and bwrap then doing its own internal clone() of the sandboxed
target. Without --unshare-pid, bwrap has little enough setup work to do
that it could reliably win that race, cloning its target before the
parent's own write into cgroup.procs completed -- leaving that target, and
everything it later spawns, permanently outside the tracked cgroup, so the
post-exit sweep found nothing to reap. Found via the user's own request to
test "pid namespace off, cgroup on" as root: confirmed directly by
inspecting cgroup.procs mid-session, showing only bwrap's own pid.
Fixed by giving run_process_foreground() a new before_exec hook, invoked in
the child synchronously right before execvp() -- the child cannot proceed
to exec (and thus cannot trigger any of bwrap's own internal forking) until
this has already returned, closing the race structurally rather than by
timing luck. run_bwrap() now creates the session cgroup there instead of in
on_start; the parent side just reconstructs the deterministic path
unconditionally, since the downstream sweep/cleanup functions already
tolerate a nonexistent directory gracefully either way.
Also fixes a false positive found while verifying this: the regression
test's own process-matching did a substring search across a whole cmdline
blob, which matched an unrelated manual `pkill -f 'sleep 137'` diagnostic
command run by hand during the investigation. Tightened to an exact
argv[0]/argv[1] match.
Finally, the regression test now SKIP()s (instead of failing) when neither
a pid namespace nor a working session cgroup is available for the current
effective config -- a documented, known residual limitation, not a
regression -- checked directly via two new helpers rather than assumed from
e.g. geteuid().
ceamac
e047d243f2